Can I reduce the header height? If so, I would like to reduce it to about 1/2 of its size or even 1/3. What's the code I would put in Custom CSS? This is mainly because the header is taking up too much real estate in the mobile version.

Thank you - I was able to adjust the height. But I added the same number -10px to the -10% to follow instructions on maintaining responsiveness, and the header and nav bar separate on mobile display. The ipad display is fine. This is the code I've added to Custom CSS: